How does an Indiglo timepiece function?

The fundamental principle behind the Indiglo watch is electroluminescence, a process where electricity is directly transformed into light.

This is not how traditional incandescent bulbs operate. In an incandescent bulb, electricity generates heat, which in turn produces light. Electroluminescence, however, is more efficient as it directly converts electricity into light.

A common example of electroluminescence that we frequently encounter is a neon light. In neon lighting, high voltage excites electrons within neon atoms, and when these electrons return to a lower energy state, they release photons.

In an Indiglo watch, a thin panel is energized by high voltage to activate phosphor atoms that emit light. The structure of the panel is quite simple. According to the Timex patent, it involves taking a thin layer of glass or plastic, coating it with a transparent conductor, layering it with a very thin phosphor coating, covering it with a thin plastic layer, and adding another electrode. Essentially, two conductors (forming a capacitor) are positioned with phosphor in between. When 100 to 200 volts of AC (alternating current) is applied, the phosphor becomes energized and begins to emit photons.

Generating high voltage in a wristwatch presents a challenge, as the watch is powered by a small 1.5-volt battery. To achieve the 100 to 200 volts needed, a 1:100 transformer is utilized. By charging the transformer's primary coil with a transistor that switches on and off, the secondary coil can reach around 150 volts.

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